Add a codestyle for Android Studio / intellij.

Copied from Android Open Source Project at
https://github.com/android/platform_development/commit/87cfafaa3d9ebebe6a60d7919fe6b4dfb62a7bf0

Update HACKING.md to describe how to install and enable this style in
Android Studio.
Remove unused imports.
Convert mScanBtn to a local variable instead of a field.
Remove unnecessary semi-colons.
Remove redundant local variables.
Remove empty onCreateOptionsMenu() method.
Suppress EmptyMethod warnings for onPreExecute() and onCancelled().
Remove redundant initialiser.
Remove redundant "artwork" variable.
Add pragma to disable warning for valid empty if() body.
Remove empty switch statement.
Remove unused variable "parameters".
Use 0dip instead of wrap_content for more efficient layout_height.
Use "sp" instead of "dp" for textSize to honour user's preferences.